Study on the Decontamination of Contaminants in Polyethylene Terephthalate by Supercritical Carbon Dioxide: From the Perspective of Molecular Descriptors.

The escalating issue of global plastic pollution necessitates the development of efficient and sustainable recycling technologies, particularly for producing safe, food-contact-grade recycled plastics. Within a circular economy framework, polyethylene terephthalate (PET) holds significant promise due to its excellent recyclability. However, contaminants introduced throughout its lifecycle pose a major challenge, and conventional decontamination methods often involve high energy consumption, thermal degradation risks, or chemical residues. Supercritical carbon dioxide (scCO2) emerges as a promising green alternative, yet a systematic understanding of its efficacy, especially from a molecular structure perspective, is lacking. This study therefore aims to comprehensively evaluate the decontamination performance of scCO2 on PET contaminated with 44 representative contaminants and, crucially, to elucidate the intrinsic relationship between decontamination efficiency and molecular descriptors of the contaminants. The results demonstrated that scCO2 achieved high removal efficiency (>95%) for most contaminants within a short treatment time (<30 min). Correlation analyses of decontamination efficiency with the 126 molecular descriptors as well as the five-solute ESABV descriptor system both revealed that contaminants with high sp3-hybridized carbon content, flexible aliphatic chains, and uniform electrostatic distributions were readily removed, whereas those with aromatic rings, strong hydrogen-bonding propensity, and rigid conformations exhibited lower efficiency. The introduction of ethanol as a cosolvent enhanced the removal of recalcitrant contaminants. Furthermore, scCO2 outperformed conventional vacuum decontamination for over 90% of the substances. This work establishes a critical structure-efficiency relationship, providing a theoretical foundation for optimizing scCO2-based processes to achieve food-grade recycled PET and advance sustainable plastic recycling.